1. **State the problem:** We have a curve with equation $$y = x^3 + ax + b$$ and stationary points at coordinates $(2, k)$ and $(-2, 10 - k)$. We need to find the values of $a$, $b$, and $k$.
2. **Recall the formula for stationary points:** Stationary points occur where the derivative of the function equals zero. The derivative of $$y = x^3 + ax + b$$ is $$y' = 3x^2 + a$$.
3. **Find $a$ using the stationary points:** Since $(2, k)$ and $(-2, 10 - k)$ are stationary points, their $x$-coordinates satisfy $$y' = 0$$.
Set $$y' = 0$$ at $$x=2$$:
$$0 = 3(2)^2 + a = 3 \times 4 + a = 12 + a$$
Solve for $a$:
$$a = -12$$
4. **Use the original function to express $k$ and $b$:**
At $x=2$, $$y = k$$, so:
$$k = (2)^3 + a(2) + b = 8 + (-12)(2) + b = 8 - 24 + b = b - 16$$
At $x=-2$, $$y = 10 - k$$, so:
$$10 - k = (-2)^3 + a(-2) + b = -8 + (-12)(-2) + b = -8 + 24 + b = b + 16$$
5. **Solve for $k$ and $b$ using the two equations:**
From the first:
$$k = b - 16$$
From the second:
$$10 - k = b + 16$$
Substitute $k$ from the first into the second:
$$10 - (b - 16) = b + 16$$
Simplify:
$$10 - b + 16 = b + 16$$
$$26 - b = b + 16$$
Add $b$ to both sides:
$$26 = 2b + 16$$
Subtract 16:
$$26 - 16 = 2b$$
$$10 = 2b$$
Divide both sides by 2:
$$\cancel{2}b / \cancel{2} = 10 / 2$$
$$b = 5$$
6. **Find $k$ using $b=5$:**
$$k = b - 16 = 5 - 16 = -11$$
**Final answers:**
$$a = -12, \quad b = 5, \quad k = -11$$
Stationary Points 25027E
Step-by-step solutions with LaTeX - clean, fast, and student-friendly.